In this paper we discuss the basic characteristics and performance of precision washing using ER water (electrolyzed reducing water) electrolyzed with Na₂SO₄ solution (Na₂SO₄ ER water). First, the structure and characteristics of the three-tank system used to produce electrolyzed water as well as how Na₂SO₄ ER water is produced by the system are described. Next, the relationship between the characteristic value of Na₂SO₄ ER water and the electrolytic current, and its difference from those for NaCl ER water and NaOH solution are investigated experimentally. Changes in the characteristic value of Na₂SO₄ ER water with time are also investigated in the same time. Finally, according to the results of washing the surface of precision parts with Na₂SO₄ ER water, C₉H₁₂ solution and pure water, the washing efficiency of Na₂SO₄ ER water is verified.